I have not built one but have been thinking the same thing as I just picked up a Combustioner myself, cant wait to use it. It is all I can do to stop myself from taking the hammer to the ton of lump in my basement to make stoker. I guess the only thing to worry about in building such a little crusher is the fines. Although your post just made me think of one possible solution, although I think it may crush too small, is the small sample crushers that coal labs use to process coal samples. They can handle 5 gallon buckets of coal at a time so it would make quick work of most anything. Just a thought.